function animate(obj,target,callback){
    clearInterval(obj.timer)
    obj.timer=setInterval(function(){
        var step = (target - obj.offsetLeft)/10
        step = step>0?Math.ceil(step):Math.floor(step)
        if(obj.offsetLeft===target){
            clearInterval(obj.timer)
            if(callback){
                callback()
            }
            
        }
        obj.style.left = obj.offsetLeft + step +'px'
    },10)
}